For Aristotle, all things in the universe have a purpose or end, and that purpose expresses the most complete form its nature can take. For instance, the purpose of an acorn is to become a thriving oak tree, just as the purpose of a harpist is to play the harp well. What is the purpose of a human being? There is a function specific to human beings, something that distinguishes us from all other beings. That function is reason and so our purpose must be to cultivate reason as best we can. Living life according to reason is our purpose and living an excellent life is to reason well and act accordingly. To achieve such a life is to achieve happiness. It is our ultimate purpose, the end to which all other goals are subordinate. (…)
Of course, there is more to our nature than rationality. We have emotions, desires and a variety of needs that we must satify. For Aristotle, in order to live a flourishing life, we have to develop all of our capacities and potential. The role of reason is to govern this process of development, to intergrate our various capacities and direct them towards their perfection. If one leads a flourishing life, then one is likely to experience a good deal of pleasure and develop positive attitudes towards one’s life. But these subjective elements are byproducts of happiness, they do not define it. Happiness is not a state of mind. Rather, it is the condition of having fulfilled one’s human potential.
Furrow, Dwight, Ethics: Key Concepts in Philosophy. Continuum, 2005, s. 115-116